The present invention is concerned with hybrid powertrains for vehicles, i.e. the combined devices needed for propelling vehicles including engines, motors, mechanical transmission means such as shafts, gears, axles, etc., and finally the exterior driving devices such as wheels and tires acting by friction on a surface of the ground such as that of a road.
A powertrain or drive train for a vehicle generally comprises some kind of motor or thermal or heat engine producing a mechanical force or torque and some transmission means converting the force or torque to a movement of the vehicle. The transmission means thus normally comprise a gear box or generally some mechanical conversion means, the wheels of the vehicle and various shafts from the motor and between the components of the transmission means. Such powertrains for vehicles can use a one or two electric motors which are capable of driving the vehicle at least at moderate power levels using energy stored in an electric energy storage unit such as an electrochemical accumulator and at the same time such a powertrain can use a thermal engine to charge the electrical storage system and to possibly supply extra power during time periods when high power levels are required. Alternatively the thermal engine can ordinarily drive the vehicle and simultaneously charge the energy storage, from which power is supplied to an electric motor when extra driving power is required. This kind of powertrains using two different motors of quite different types is called hybrid powertrains.
Classical hybrid powertrains comprise two basic types, the serial type, the construction of which is schematically illustrated in FIG. 1, and the parallel type, the construction of which is schematically illustrated in FIG. 2.
In the SEV (xe2x80x9cSerial Hybrid Vehiclexe2x80x9d) system illustrated in FIG. 1, an electric motor 101 directly drives the wheels 108 of a vehicle and thus provides all of the power required by the wheels for propelling the vehicle. The electric motor receives electric power from an accumulator 104. At high power levels, the thermal engine 103 is activated to drive a generator 102 and thus adds through the generator additional power to the accumulator, this additional power being the difference between the power required by the electric motor and the power which can be directly taken from the accumulator. At least for longer trips, the thermal engine 103 and the generator 102 will when required charge the accumulator 104 and thereby supply most of the power required by the electric motor 101 for driving the wheels.
In most applications, a mechanical reduction 105 is used to allow the use of electric motors 101 having a lower torque and a higher speed than what is normally required for driving the wheels 108. The mechanical reduction 105 is thus connected between the electric motor 101 and the wheels 108. However, the electric motor 101 must be dimensioned to provide all the power required by the wheels at all times, and a torque which varies linearly with the torque of the wheels.
Serial hybrid vehicle systems of the kind described above are often designed to use small thermal engines which are dimensioned to be capable of providing little more than the average power required for driving the vehicle on a horizontal highway at high speeds, such as in typical designs about some 10 kW. This permits the thermal engine to work either at an optimum load point or not at all, thereby keeping its average efficiency close to an optimum point. During accelerations and short inclinations a much higher power is taken from the accumulator, which can be an electro-chemical battery, a flywheel, a supercapacitor, etc. Long heavy inclinations require a high power over a long time period for driving the vehicle, what in turn either requires a thermal engine having a high output power or an accumulator having a high energy content.
In the PHV (xe2x80x9cParallel Hybrid Vehiclexe2x80x9d) system as schematically illustrated by the block diagram of FIG. 2 a thermal engine 203 is connected to convey a torque to the differential gearing and wheels 208 through a disengageable clutch 207 and a gearbox 206. The gearbox 206 can also receive input torque from an electric generator/motor 201 through an optional mechanical reduction 205. The electric generator/motor receives its input power from an energy storage unit or accumulator 204. The torques provided by the thermal engine 203 and the electric generator/motor 201 are thus both input to the gearbox, this implying that also torque can be provided from e.g. the thermal engine 203 to the electric generator/motor 201, when there is sufficient power available in the thermal engine. In such cases the accumulator can be charged by the electric generator/motor which then operates as a generator.
Generally, the accumulator 204 and the electric generator/motor 201 and its electronic drive circuits, not shown, have to provide a power being the difference between the power required for driving the wheels and the power which is provided by the thermal engine 203. In many applications, a mechanical reduction 205 is used to allow the use of electric motors having a lower torque and a higher speed than those provided by the thermal engine.
When the thermal engine 203 is switched off it is also disconnected from the wheels by operating the clutch 207. All of the traction power is in this case supplied from the energy storage 204 through the electric motor 201 which can also work as an electric generator. The energy storage 204 can, as has already been mentioned, be charged by the thermal engine 203 while the vehicle is running. The parallel hybrid vehicle system as described above has the disadvantage that the speed of the thermal engine 203 is dependent on the speed of the tires of the wheels and the setting of the gearbox 206 and therefore the thermal engine has a non-constant speed during running and then also during charging the energy storage or accumulator 204. The torque of the thermal engine 203 can however be maintained at a suitable value by selecting a suitable torque (positive or negative) for the electric generator/motor 201. As the engine will loose its load as soon as the clutch is disengaged, the torque of the thermal engine 203 must change quickly as soon as a gearshift is performed. For many thermal engine designs, this operation in addition causes high peaks of environmentally unwanted emissions.
Parallel hybrid vehicle systems are disclosed in U.S. Pat. Nos. 4,533,011, 5,337,848, 5,492,189 and 5,586,613.
In FIGS. 3a and 3b block diagrams of two hybrid systems are shown which can be described to be mixtures or combinations of the serial hybrid vehicle systems and the parallel hybrid vehicle systems as described above. Employing the terms used in the published European patent application EP 0 744 314 A1 they can be called PSHV (xe2x80x9cParallel Serial Hybrid Vehiclexe2x80x9d) systems.
The parallel serial hybrid vehicle system illustrated by the block diagram of FIG. 3a is described in the cited EP 0 744 314 A1, see the description of FIG. 9 in this document. The system according to FIG. 3a has the advantage that it to some extent can use both the advantages of a serial hybrid vehicle system and a parallel hybrid vehicle system. Here the thermal engine 303 has an electric generator/motor 309 directly mechanically coupled to its output shaft, not shown. To the output shaft is also an electric motor 301 connected but through a clutch 307. The output shaft thus drives through the clutch 307, when it is engaged, the differential gearing and the wheels 308. The electric generator/motor 309 and the electric motor 301 can when required be powered by the electric energy storage 304 and the electric generator/motor 309 can also charge the energy storage.
When the clutch 307 is disengaged and freely running, the vehicle system of FIG. 3a acts as an SHV system and gives a constant or slowly varying load on the thermal engine 303, permitting a high thermal engine efficiency and low emissions. When the clutch 307 is engaged it gives the advantage of a PHV system, i.e. a higher power transfer efficiency between the thermal engine 303 and the wheels 308. As pointed out in EP 0 744 314 A1, see column 4, lines 6 ff., the last advantage is only applicable for medium to high speed vehicle movements since the rotation speed of the thermal engine and thus of the electric generator/motor 309 at low vehicle speeds will be below the lower operational limit of the rotational speed of the thermal engine.
In FIG. 3b a block diagram of a PSHV system is shown in which the speed of the thermal engine 303 is independent of that of the differential and wheels 308. The system of FIG. 3b is obtained from that depicted in FIG. 3b by replacing the electric generator/motor 309 with a planetary gear 310, the planetary gear instead driving or being driven by the electric generator/motor 309. The thermal engine 303 thus drives the differential gearing and the wheels 308 through this planetary gear 310 and the clutch 307, when the clutch is engaged.
In the state in which the thermal engine 303 drives the wheels, the system can for analytic purposes be regarded as three blocks, the first block of which is the thermal engine 303. The second block 311 consists of the planetary gearbox 310, the electric generator/motor 309 and a first aspect of the electric motor 301. The second block operates as a continuously variable transmission between the thermal engine 303 and the differential and wheels 308. It transfers the power from the thermal engine 303 from one speed/torque combination suitable for efficient and environmentally good operation of the thermal engine 303 to another speed/torque combination suitable for the differential gearing/wheels 308. The output torque of the second block will be determined by the input torque and the speed relation of the input and output shafts of the second block. The mechanical energy at the input shaft of the second block minus conversion losses will appear at the output shaft thereof as it would in a purely mechanical, continuously variable transmission.
The third block consists of a different, second aspect of the electric motor 301, which adjusts the output torque from the variable transmission block 311 to the torque required by the wheels. It does this by converting power from the accumulator 304 to a mechanical torque and adding this extra mechanical power to the shaft of the motor 301 or by converting excess mechanical power at the shaft to electric power and charging the accumulator 304. The physical electric motor 301 is required to provide a torque which is the sum of the two torques attributed thereto as a component of both the second block and the third block in the analysis given above.
The hybrid powertrain according to FIG. 3b has the advantage of allowing that part of the power of the thermal engine 303 can be transferred by a highly efficient mechanical path from a the thermal engine 303 to the differential and wheels 308 and still permitting the thermal engine 303 to run at a slowly varying speed. The thermal engine speed and torque can therefore be selected to optimize thermal engine efficiency and polluting properties independently of the speed and torque of the differential gearing and wheels 308.
It is an object of the invention to provide a PSHV system having a high overall efficiency path from a thermal engine of the system to the wheels of a vehicle.
Another object of the invention is to provide a PSHV system which permits a thermal engine of the system to operate at a high overall efficiency.
Another object of the invention is to provide a PSHV system which avoids variations of speed and torque of the thermal engine faster than what is compatible with goals for emissions and efficiency.
Another object of the invention is to provide a PSHV system which gives an acceptable performance if the accumulator and/or electric motor system capacity should be reduced or even if the accumulator and/or electric motor system cease to operate.
Another object of the invention is to provide a PSHV system, which is capable of recharging its accumulator even when the vehicle is stationary.
Another object of the invention is to provide a PSHV system having a long service life and a low cost, in particular a PSHV system having a dramatically reduced slip and other moving friction forces on components like clutch and gearbox components during shifts of gear position or speed.
Another object of the invention is to provide a PSHV system capable of driving a vehicle when ascending long steep slopes.
Another object of the invention is to provide a PSHV system capable of braking a vehicle when descending long steep slopes.
Another object of the invention is to provide a PSHV system which is capable of providing occasional high output power peaks using electric motors and thermal engines having comparatively modest power ratings.
Another object of the invention is to provide a PSHV system which makes use of investments already made in designs and automated equipment for manufacturing vehicles.
Another object of the invention is to provide a PSHV system which permits the use of electric motors of the permanent magnet type having considerable losses when spinning or rotating at low loads without obtaining high losses during high vehicle speeds.
The problem solved by the invention is how a hybrid powertrain of the combined serial and parallel type can be constructed which as improved performance, in particular a reduced fuel consumption and a high total efficiency. Thus a powertrain for a vehicle is the combined serial and parallel hybrid type as generally defined above. It comprises a thermal engine, an electric generator/motor mechanically coupled to the output shaft of the engine, a coupling device such as a clutch which can connect the output shaft to the wheels for driving the vehicle. Thus, the output shaft can be divided in two portions, the coupling device connecting the two portions rigidly to each other when required. An electric motor/generator is mechanically connected to the wheels for driving them when required. It can be connected to the distant portion of the output shaft, which can be disconnected from the near portion by operating the coupling device. The clutch can connect the output shaft of the engine to the input shaft of a gearbox, the output shaft of which is connected to the wheels of the vehicle through a differential. An electric motor is mechanically connected to the differential or the gearbox input- or output shafts. Both the generator/motor and the electric motor can be driven by the thermal engine to charge an electric accumulator and can receive electric power therefrom to provide extra torque. The term xe2x80x9cmechanically connectedxe2x80x9d means that the electric motors have the motion of their rotation shaft coupled to the respective shaft, such as having a common shaft, interacting through a gearing, a belt, etc.
Generally, a powertrain of a vehicle comprises a mechanical gear box and at least one thermal engine, ordinarily only one, having an output shaft, which shaft when required can be mechanically connected to at least one of the wheels of the vehicle through the mechanical gear box for driving the at least one of the wheels. Furthermore it comprises an energy storage and at least one engine side electric motor and at least one tire side electric motor. At least two different electric motors are thus provided and they are connected to the energy storage and are supplied with electric power from the energy storage for providing or receiving mechanical power or torque when required. Connection means are connected to the electric motors, to the output shaft of the thermal engine and to the wheel or wheels for mechanically connecting the engine side electric motor to the output shaft of the thermal engine to be driven by the thermal engine and for mechanically connecting the tire side electric motor to the wheel or wheels for driving it/them.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the methods, processes, instrumentalities and combinations particularly pointed out in the appended claims.